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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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GIACIATION OP LOWER COPPER RIVER
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west and the outwash plain of Martin River Glacier on the east. The Copper River delta merges so imperceptibly with the outwash gravels which fill the former Copper River fiord that it is best thought of as heading at Quids and Miles Glaciers, especially because just below Goodwin Glacier the Copper River branches into a series of distributaries.
Details Regarding the Glacial Strearfis on the Delta. At present the Copper River distributaries occupy the western half of the delta and the Martin River distributaries the eastern half. The largest of the Copper River channels follows the extreme western side of the valley and at the lower bridges on the Copper River and Northwestern Railway there are smaller branches east of Long Island, the chief one called Hotcake Channel; and two main streams west of Long Island, separated by Round Island. We shall call the westernmost and largest of these the Flag Point Channel and the smaller or eastern distributary, between Round and Long Islands, the Long Island Channel. Round and Long Islands each rise SO to 60 feet above sea level, or 12 to 48 feet above all stages of water, and there are numerous sand bars at their borders at the lower stages of the river.
The combined width of these three chief distributaries of Copper River is 4445 feet, in contrast with a width of 1600 feet in the single channel of the undivided river at Miles Glacier bridge, where the depth is not much greater but the velocity is several times that at Flag Point Channel. The relationships of width and depth and velocity are shown below, the total volume of the river having increased slightly below the Miles Glacier bridge by receiving water from the Childs, Goodwin, and smaller glaciers. In this table high water widths and depths are used, but the velocities are determined at various stages of river and are not so directly comparable.
TABLE SHOWING WIDTHS, DEPTHS, AND VELOCITIES or COPPHB RIVEB ON ITS DELTA
Name of Channel	Width of River . in Feet	Depth of River in Feet	Velocity in Miles per Hour
Miles Glacier Bridge Flag Point Channel Round Island Channel Hotcake Channel	1500 3200 535 720	33 to 40 6 to 29 30 18	6 to 12 2.8toS.6 3. 2 to 3. 4
			
It may be of interest to compare and contrast the conditions at the head of the Copper River delta, where the river is in a single channel, with those at the three distributaries to the south. For this purpose data must be taken from (a) the channel at Miles Glacier Bridge and (b) at a point just south of Childs Glacier.
At Miles Glacier bridge, where there is a 1550 foot steel bridge, the river level varies from' 116 to 140 feet above mean low tide at sea level, giving a vertical annual range of 24 feet. The channel is 8 to 16 feet deep at low water, when it is divided by a great gravel bar. At low water the velocity of the current is 3 to 3.8 miles an hour, but even